Historically, planting small seeds was a labor intensive job. Methods such as broadcasting, where the seeds would be scattered onto a field, were typically employed. Needless to say, the seeds were not spaced properly by this method. Thus, expensive and time-consuming labor would be required to thin the plants after the seeds had sprouted to prevent the plants from inhibiting the growth of neighboring plants. Further the seeds are not efficiently planted since thinning is required. Further the random nature of planting resulting from broadcasting detracts from automated cultivation since row and plant spacing may be non-uniform.
Another technique was to adhere the seeds in a spaced relationship on a fabric or paper planting tape which is rolled into a furrow and covered. These planting tapes are typically of a short length, e.g. 5 feet for a garden strip or a field strip may be 100-1000 feet, which therefore requires a great deal or labor to place and string planting tapes together end-to-end to plant a large field. However, planting tapes provide for efficient and labor saving planting of seeds since the amount of thinning is reduced due to the spacing of the seeds on the tape and the confining of the seeds to the rows defined by the planting tape.
A variety of devices have been invented to more accurately meter and dispense seeds. For example, Loesch et al. (U.S. Pat. No. 3,637,108) discloses a seed planter in which seeds are deposited into holes in a drum. A positive pressure holds the seeds in place while they are conveyed to a position to be mechanically dislodged from the holes or dislodged by a burst of air to fall into discharge tubes where the seeds are dropped. The seeds are carried down the tubes by the air under pressure in the drum. One of the drawbacks of this arrangement is that the device is complicated requiring seals about the discharge tubes whose ends extend into the drum. Further, for light seeds the turbulents within the drum created by the positive pressure may prevent the seeds from being directed into the discharge tubes or effectively carried to the desired location for disposition.
In Romans (U.S. Pat. No. 5,392,707) a vacuum is used to draw a seed into pockets in a rotating wheel. The wheel transports the seeds to a position where the vacuum is relieved and the seeds fall by their own weight for planting. One of the drawbacks of this device is that small, light seeds may not fall when the vacuum released and may tend to stick to the wheel due to static attraction caused by the flowing air of the the discharge openings.
In Holland (U.S. Pat. No. 4,688,698) a seed dispensing mechanism is disclosed which imposes a vacuum to pick up seeds in an etched plate and drops the seeds by releasing the vacuum. The etched apertures in the rotating plate are arranged radially whereupon entire rows of seeds are released. A drawback of this type of device is that there is no positive ejection of the seeds to permit more precise placement. The seeds fall due to gravity which, for lighter and smaller seeds, may result in inadvertent dispersal as a result of wind, dust and the like. Further, the mass dropping of entire rows of seeds further detracts from precise placement of seeds in the soil or on planting strips.
Significantly, the devices in the prior art, are not well suited for dispensing small seeds such as garlic, celery and the like. Those prior devices rely on the weight of the seed to release the seed for planting are not suitable in that the smaller seeds may adhere to components due to electrostatic attraction or may be dispersed by wind not only of environmental sources but due to turbulents from the planting equipment such as the tractor, plow or the like. It is further clear that small seeds may be so light that the weight of the seed itself is not enough to dislodge the seed from the seed carrier. Moreover, the weight of the seed may not be enough to force the seed through the dispensing tube, thereby creating a blockage in the dispensing tube. Still further the devices of the type described above tend to dispense seeds en masse which further frustrates more precise planting and disposition on planting tapes.
Still further, the devices described above are operated by either a vacuum or by positive pressure. A significant portion of the energy of compression is lost by only using the discharge side of the vacuum pump or compressor to operate the device.
Thus, it can be appreciated that there is a need in the art for a device which can meter and dispense small seeds accurately for planting and for use on seed tapes, which is of simple construction and is energy efficient.